Flood and water damage occurs worldwide to homes and businesses. It typically occurs from leaking pipes, burst water hoses, and plugged drains, but can also be the result of flash floods and storm surges. Timely intervention can minimize the destruction especially to minimize mold and mildew, and cost to repair, which can be considerable. Water damage could be significantly reduced if sensors could be deployed to monitor likely areas for water problems: basements, kitchens, bathrooms. These sensors could sound a local alarm or could be linked to home or business security systems and signals transmitted to a security company or the local fire and police departments.
Known types of sensors are typically direct contact type electrical sensors which monitor changes in capacitance or conductivity as a result of being immersed. Such sensors are placed on the floor and must be covered by several millimeters of water for detection to occur. They can get in the way of foot traffic, can corrode, and may not detect at all if water flows around them without touching them.
An example of the electrical contact sensor is given in U.S. Pat. No. 4,266,195, by G. H. Utke. Likewise, U.S. Pat. No. 7,696,889, titled Fluid Leak Detection System and Associated Method, and U.S. Pat. No. 7,239,246, titled System and Method for Detecting Water Leakage, disclose electrical sensing methods. A device to sense a drop in water pressure when there shouldn't be one is described in U.S. Pat. No. 7,306,008, titled Water Leak Detection and Prevention System and Methods. U.S. Pat. No. 7,562,673, titled Automatic Flow Shut-off System, describes a water heater with a collection pan under it containing a shut off valve. When the valve body gets wet, the paper holding the valve open disintegrates and the valve closes to shut off the water supply. Another device with a similar collection pan is described in U.S. Pat. No. 6,414,598, titled Liquid Leak Detector and Alarm System, where a float in the collection pan rises with a leak and causes the water to shut off. All of the above patents require direct contact with the water or a water pipe.
U.S. Pat. No. 7,224,453 titled Device, Method and System for Determining the Road Surface Condition, describes an optical method in which a frequency modulated spectrometer is directed at the road surface, and the return signal at the frequency of the modulation and twice the frequency of modulation is detected and compared. Such a system, while non-contact, is complex, expensive, and operates differently than the present invention.
There are several pending patent applications that describe water detection systems using electrical sensors, such as U.S. Patent Publication No. 2009/0207031, titled System and Method for Detection of a Variety of Alarm Conditions, and U.S. Patent Publication No. 2007/0024458, titled Water Detection Unit and System. A microphone to sense running water and determine if the water, e.g. toilet, has been running too long, is described in U.S. Patent Publication No. 2009/0224927, titled Running Water Detection and Alert Device for Plumbing Fixtures. It is primarily aimed at toilets whose float valve has stuck.
U.S. Pat. No. 4,690,553 titled Road Surface Condition Detection System, describes a system having a light projector operating in a 1400 to 2500 nm IR range mounted on an arm over a road surface at a different angle with respect to two light sensors. As indicated in FIG. 3 of this patent, such IR range is optimal for detecting a drop in the amount of scatter reflected light from the road surface (i.e., a high signal to noise ratio in the signals from the light sensors), but use of IR range below 1000 nm would negatively affect sensitivity to detect wetness, snow, or ice, since the drop is scatter reflected light and would be difficult to detect. Further, mounting the system of this patent in a home or building, rather than over a road surface, is not practical.
One problem with a non-contact detection system is that ambient light can overload the system, which hinders the detection of reflected light by a light sensor emitted from a source. This problem is especially acute in a non-contact optical detection system using light source operating in the IR range below 1000 nm having a poor signal to noise ratio response when detected. Although light sources, such as light emitting diodes (LEDs) operating in the longer wavelength IR range (1450 nm-1560 nm) are desirable as the source (and also as the detector), since they provide illumination enabling a high signal to noise ratio in the detected signal by a detector sensitive in the same IR range. The problem is that these LEDs in the longer wavelength IR range are expensive as compared to typical low cost LEDs that operate at shorter IR wavelength ranges (940 nm-970 nm). However, use of such low cost LEDs is problematic in that their shorter IR wavelength range is about 100 times less absorbed by water than LEDs in the longer wavelength range, thereby undesirably causing a low signal to noise ratio in the detected signal, severely diminishing sensitivity to water detection, thus making the use of such low cost LEDs heretofore impractical for water detection for example if such were used in the system of U.S. Pat. No. 4,690,553. Thus, it would be desirable if a non-contact water detection system could be made at a lower cost by utilizing lower cost LEDs emitting light at a shorter wavelength IR range, while providing improved sensitivity to detection of water (liquid or moisture), which is further capable of detection of other liquids, or water vapor, ice, mist and other gases, on a surface.